Reflective displays require a front light system to facilitate viewing of images displayed. The front lighting for reflective displays normally consists of a light guide film attached to the front surface of the display. This light guide film has an illumination source placed at the edge of the light guide film and the light is guided within the film by total internal reflection of the surface along the light guide film, so that the light crosses the front of the display. Part of the surface of the light guide has a light scattering structure which causes light inside the light guide film to be scattered out of the film to strike the display surface. Such a system usually has a slightly rough surface which may be the display itself that is index matched to the light guide film, or has an array of microprisms specifically designed for this purpose. The display illuminated by the scattered light is viewed by looking through the light guide film.
Such a front lighting system has many disadvantages. First, since the light is strongest at the point of entry into the light guide film, the light tends to fall off in intensity rapidly at points which are further from the illuminating source. To compensate for this, a very complicated light prism structure may be utilized. This light prism structure may have different amounts of scattering near the source and at the points away from the source. Although such a system provides some degree of improvement in lighting uniformity, the uniformity, however, is still unsatisfactory, and the system must be customized for every application. Secondly, since this lighting system is based on scattering phenomenon, any scratch or piece of dirt in the light guide film also scatters the light which shows up as defects. As a result, it is very difficult for such a system to function properly. In addition, if a flexible front light is required, the front light system must be very thin; but a thin front light guide film exacerbates non-uniformity of the light along the length of the light guide film as described above.